With the decrease in size and increase in functionality of portable electronic devices in recent years, further miniaturization, weight reduction and higher capacity are expected for electrochemical elements.
Electrochemical elements can be made into various forms. A prismatic type, a pillared type and a pouch type or the like can be listed as the representative ones.
Among them, the pouch-type electrochemical element uses a pouch-type case made by sheets such as aluminum laminate film or the like, thus, it is light and can be manufactured into various forms. There is also a strong point in the simple manufacturing process. On the other hand, compared with the pillared type and the prismatic type, the pouch-type has a problem that it is easy to swell due to a flaw or an increase in the inner pressure.
In the electrochemical elements, in a lithium ion secondary battery or a lithium ion capacitor, a mixed solvent of a ring carbonate such as ethylene carbonate and a chain carbonate such as diethyl carbonate is usually used as the electrolyte solvent; in the electric double layer capacitor, acetonitrile, propylene carbonate or the like is used as the electrolyte solvent; and in aluminum electrolytic capacitor, ethylene glycol or the like is used as the electrolyte solvent. When the sealability of the case of the electrochemical element is insufficient or when a pinhole or the like occurs in the case, a part of these solvents will become vapor and be evaporated and there will be problems such as bad smells leaked from the hermetically sealed container or deterioration of the properties.
Various detection methods for leaked gas from the hermetically sealed container are proposed up to the present.
For example, in Patent document 1, a detection method is proposed for detecting the leaked detected gas from the hermetic battery using a gas sensor by manufacturing a hermetic battery in a hermetically sealed container with a detected gas atmosphere such as helium or argon or the like and then removing the detected gas in the hermetically sealed container followed by decompressing.
However, in the detection method of Patent document 1, a hermetically sealed container is required in the manufacturing process, thus, not only the instrument will be in a large scale, but also a detected gas supplying, pressure reducing devices and processes such as sensing for detected gas using a sensor are required. Therefore, there is a problem that the detection cannot be carried out simply. Further, there is a problem that the gas leakage before or after the detecting process cannot be detected.
In addition, in Patent Document 2, a method of detecting a gas in an atmosphere using a gas detection tube which will change color by reacting with a gas component is proposed. However, although it is possible to detect the leakage of the gas from the electrochemical element into the atmosphere, there is a problem that it is impossible to determine the gas leaking position.